Primates, including humans, explore their visual environment with sequences of gaze fixations interrupted by saccadic eye movements that re-orient the fovea to objects of interest. This visual behavior is thought to involve two separate processes. First, the current foveal image is analyzed and the next object of interest is selected as a saccade target. Second, previously examined objects are retained to prevent their re-examination. Visual behavior has been studied successfully using the visual search paradigm, in which subjects locate a unique target stimulus from amongst multiple distracting stimuli. Models of visual search posit that the process of saccade target selection is guided by a visual salience map. This map receives both stimulus-driven and goal-directed inputs to form representations of visual objects, and a competition between those representations is played out to determine the next saccade target. Neurophysiological studies using nonhuman primates have suggested that the salience map is distributed across a network of brain areas that includes the midbrain superior colliculus (SC). These studies, however, have not ruled out the possibility that selective activity for a saccade target may instead be related to the preparation of the saccade. Moreover, not much is known about the selection of a saccade target beyond the first in a sequence of gaze fixations. Finally, the mechanisms underlying the process of saccade target retention are not well understood. In this thesis, I will investigate the role of the primate SC in visual behavior by recording the activity of single neurons while monkeys perform visual search tasks. The major findings will describe 1) how SC sensory-motor neurons instantiate the visual salience map; 2) how this salience map is dynamically updated so that saccade targets are retained; and 3) how multiple representations on this salience map are processed in parallel for saccade target selection. Given SC’s role in the control of visual behavior and its position within the network involved in cognitive processes, these findings have important implications for our understanding of the neural basis of human cognition and of its dysfunctions in disease states. / Thesis (Ph.D, Neuroscience Studies) -- Queen's University, 2010-12-22 09:52:20.143

Emotionally charged stimuli have been reported as efficient distractors during visual search (e.g., Eastwood, Smilek, Merikle, 2001; Hansen & Hansen, 1988; Öhman, 2002; Öhman, Flykt, & Esteves, 2001; Öhman & Soares, 1993). The extensiveness and specificity of the influence of such distractions for attention and performance beyond the context of their presentation were currently investigated. Of interest was whether prior experiences of distraction from such stimuli influence spatial attention during a subsequent visual event. General and location-specific bases of such effects and the role of memory in modulating these were investigated. Over a series of trials, participants performed a target localization task during a prime event involving exposure to an emotionally charged distractor, or only neutral distractors. Subsequently, performance at the same task was measured when only neutral distractors were presented during a probe event. During each event, one of four shapes had to be identified and responded to as a target. Distractor images were presented within each shape outline. Whether or not the shapes were the same or different across the prime and probe event of a trial was manipulated as a test of the role of memory in modulating effects across the events of a trial. Earlier findings of immediate impairments to attention based in exposure to emotionally charged stimuli were replicated. The current study also revealed the occurrence of robust performance impairments during the probe event subsequent to the disruption of attention during the prime event. Evidence was limited in suggesting that the impairments depended on which location the emotional stimulus occupied during the prime event. Strong evidence, however, was observed for global impairments on attention across visual events, conditional on task demands being similar during both. An account of the findings which incorporates memory was suggested, whereby retrieval processes engaged during the probe event support access to the interaction history with emotionally charged stimuli during the prime event. Consistent experience with emotional stimuli requiring no response produced a prominent cognitive refraction period at the time of the probe event, requiring that attention be re-centered to the task. Less consistent experiences produced a briefer refractory period.

abstract: Previous research has shown that people can implicitly learn repeated visual contexts and use this information when locating relevant items. For example, when people are presented with repeated spatial configurations of distractor items or distractor identities in visual search, they become faster to find target stimuli in these repeated contexts over time (Chun and Jiang, 1998; 1999). Given that people learn these repeated distractor configurations and identities, might they also implicitly encode semantic information about distractors, if this information is predictive of the target location? We investigated this question with a series of visual search experiments using real-world stimuli within a contextual cueing paradigm (Chun and Jiang, 1998). Specifically, we tested whether participants could learn, through experience, that the target images they are searching for are always located near specific categories of distractors, such as food items or animals. We also varied the spatial consistency of target locations, in order to rule out implicit learning of repeated target locations. Results suggest that participants implicitly learned the target-predictive categories of distractors and used this information during search, although these results failed to reach significance. This lack of significance may have been due the relative simplicity of the search task, however, and several new experiments are proposed to further investigate whether repeated category information can benefit search. / Dissertation/Thesis / Masters Thesis Psychology 2014

In producing a user interface design to visualize search results for a digital library called Envision [Nowell, France, Hix, Heath, &amp; Fox, 1996] [Fox, Hix, Nowell, et al., 1993] [Nowell &amp; Hix, 1993], we found that choosing graphical devices and document attributes to be encoded with each graphical device is a surprisingly difficult task. By <i>graphical devices</i> we mean those visual display elements (e.g., color, shape, size, position, etc.) used to convey encoded, semantic information. Research in the areas of psychophysics of visual search and identification tasks, graphical perception, and graphical language development provides scientific guidance for design and evaluation of graphical encodings which might otherwise be reduced to opinion and personal taste. However, literature offers inconclusive and often conflicting viewpoints, suggesting a need for further research. The goal of this research was to determine empirically the effectiveness of graphical devices for encoding nominal and quantitative information in complex visualization displays. Using the Envision Graphic View, we conducted a within-subjects empirical investigation of the effectiveness of three graphical devices - <i>icon color, icon shape,</i> and <i>icon size</i> - in communicating nominal (document type) and quantitative (document relevance) data. Our study provides empirical evidence regarding the relative effectiveness of icon color, shape, and size for conveying both nominal and quantitative data. While our studies consistently rank color as most effective, the rankings differ for shape and size. For nominal data, icon shape ranks ahead of icon size by all measures except time for task completion, which places shape behind size. For quantitative data, we found, by all measures, that encodings with icon shape are more effective than with icon size. We conclude that the <i>nature of tasks</i> performed and the relative <i>importance of measures of effectiveness</i> are more significant than the type of data represented for designers choosing among rankings. / Ph. D.

No description available.

In visual search experiments, the subject looks for a target item in a display containing different distractor items. The reaction time (RT) to find the target is measured as a function of the number of distractors (set size). RT is either constant, or increases linearly, with set size. Here we suggest a two-stage model for search in which items are first selected and then recognized. The selection process is modeled by (a) grouping items into a hierarchical cluster tree, in which each cluster node contains a list of all the features of items in the cluster, called the object file, and (b) recursively searching the tree by comparing target features to the cluster object file to quickly determine whether the cluster could contain the target. This model is able to account for both constant and linear RT versus set size functions. In addition, it provides a simple and accurate account of conjunction searches (e.g., looking for a red N among red Os and green Ns), in particular the variation in search rate as the distractor ratio is varied.

Visual search consists of locating a known target amongst a field of distractors. Often times, observers must search for more than one object at once. Eye movements were monitored in a series of visual search experiments examining search efficiency and how color is represented in order to guide search for multiple targets. The results demonstrated that observers were very color selective when searching for a single color. However, when searching for two colors at once, the degree of similarity between the two target colors had varying effects on fixation patterns. Search for two very similar colors was almost as efficient as search for a single color. As this similarity between the targets deceased, search efficiency suffered, resulting in more fixations on objects dissimilar to both targets. In terms of representation, the results suggest that the guiding template or templates prevailed throughout search, and were relatively unaffected by the objects encountered. Fixation patterns revealed that two similarly colored objects may be represented as a single, unitary range containing the target colors as well as the colors in between in color space. As the degree of similarity between the targets decreased, the two targets were more likely to be represented as discrete separate templates.

The label-feedback hypothesis (Lupyan, 2012) states that language can modulate visual processing. In particular, hearing or reading aloud target names (labels) speeds up performance in visual search tasks by facilitating target detection. The current study conceptually expands previous investigations by comparing the effect of a multimodal label presentation (i.e., an audio+visual, AV, priming label), with that of a multimodal (i.e. noise+visual, NV, label) and two unimodal (i.e. audio, A, label or visual, V, label) control conditions in a visual search task. Furthermore, the name of a category (i.e. a label at the superordinate level) was used as a cue, instead of the more commonly used target name (a basic level label), with targets belonging to one of three categories: proper weapons, improper weapons, garments. According to legislation, objects are typically classified as weapons if they are offensive per se (referred to here as proper) and if they are adapted for use as weapons or carried with the intent of causing injury (referred to here as improper), with specific regulations on their usage and possession in public spaces. However, little evidence exists on the validity of this distinction in psychology, despite a widespread recognition of the importance of psychological states and perceptions in risk assessment. These categories were found to vary for their structure, improper weapons being an ad hoc category unlike proper weapons and garments, and for the perceived dangerousness and familiarity of their exemplars, which increase from garments to proper weapons. Results of the two experiments on the label-feedback effect show an overall transient facilitation of visual search performance in the AV condition compared to control conditions. However, for improper weapons, no significant difference was found between the AV and the NV label condition, suggesting that the specificity of the superordinate label effect can be modulated by the structural properties of a category. The findings are consistent with the idea that the AV condition prompted an "up regulation" of the label, a requirement for enhancing the label’s beneficial effects, with the exception of improper weapons. They also highlight the status of the category of improper weapons and offer additional proof that sets it apart from proper weapons.

<p>Cognitive psychologists have long known that there are limitations on human information processing abilities. As such we must constantly attend to relevant information in our environment, sometimes for further processing, at the expense of other information. Visual search tasks have been used extensively by researchers who seek to understand the consequences that this selective attention process has on memory. It has been argued that the priming effects observed in efficient visual search tasks reflect specialized, short-term memory representations that differ markedly from the memory representations believed to produce priming effects in other performance tasks. To the extent that this is true, researchers must adopt a necessary level of complexity in terms of the memory models used to explain the full range of human behavior. The empirical goal of this thesis was to provide a rigorous examination of priming effects in efficient visual search, in order to determine whether such effects can be explained by reference to general, well-studied memory mechanisms that have yielded significant explanatory power in other attention and performance tasks. The results of the experiments reported here suggest that general, well-studied memory principles may be a suitable candidate explanation for priming effects in efficient visual search.</p> / Doctor of Philosophy (PhD)

Several recent studies show that previous experience can influence observers’ search strategy in a way that improves search performance. The purpose of the present study is to investigate how the experience of difficult color discriminability affects search strategies. Two participant groups either experienced difficult color discriminability in a half of the trials (i.e., hard-discrimination group) or experienced easy search in all trials (i.e., easy-discrimination group) in a dual-target search task. Participants were required to respond to the presence of a target (colored T) among distractors (colored pseudo-L). Eye movements were recorded to understand which feature information is used to guide attention, and behavioral performance was measured to compare search efficiency between the two groups. The hard-discrimination group fixated more distractors with target-dissimilar colors than the easy-discrimination group, suggesting the hard-discrimination group used shape information to guide search more than the easy-discrimination group. However, error rates and response times were not significantly different between groups. The results demonstrate that the experience of difficult color discriminability discourages observers from guiding attention by color, and encourages them to use shape information.